The last time Iraq went to the polls, in 2010, US forces were in town and insurgents hovered around the edges. Now, the foreign troops are gone, but extremism has returned to overshadow a democratic watershed in a divided country.

Banners pledging unity rise above traffic-snarled Baghdad crossroads. Politicians dominate the national airwaves with their promises of services. The 30 April election is framed as a vital self-reckoning and a chance for transformation in a society that is withered by uncertainty and the creep of regional chaos.

But few in Baghdad seem to believe the poll holds answers for voters fatigued by insurgency and held back by intractable issues, such as sclerotic public services and rampant corruption.

"Every four years, we hear from our so-called leaders when they want to hold on to their chair," said Abu Radwan, an engineer from the Karrada district in the capital. "So we give them again the power they want and they then start stealing all they want. There is nothing left for us."

Nouri al-Maliki, Iraq's incumbent prime minister, is being hailed by Iraqi commentators as a frontrunner to win a third term. He is casting himself as Iraq's sole redeemer, staring down a blazing insurgency that has led him to lose control over much of Anbar province, almost one-third of the country, since December.

Another war in Anbar is testing Maliki's security credentials. Officials in Baghdad told the Guardian that by March the Iraqi military had lost close to 1,700 members in the province. The army has failed to shake extremists linked to the Islamic State of Iraq group from the cities of Fallujah and Ramadi and is attempting to safeguard the western approaches to Baghdad – 60 miles away – from what it fears will be an attempt to advance on the capital.

Fear of extremism is a strong current of pre-election discourse, with stability considered a prerequisite for reviving the dormant service sectors. There has been little talk of other issues, such as roads, sewerage, housing and electricity.

Reconciliation – another touchstone issue – has been largely ignored by almost all those vying for a place in the 328-seat parliament.

Nikolay Mladenov, the UN's envoy to Baghdad, recently warned that polarisation would jeopardise investment and could further inflame violence. Iraq's legislators say worsening violence is likely to favour Maliki's chances of a third term.

"They are working this [extremist] line very hard," said a supporter of the incumbent leader. "But this isn't getting very far with the Sunnis. They will be left out again and this is a very big problem."

Iraq's sectarian schism remains largely unreconciled, even seven years after the worst of the civil war, with its fratricidal violence between Sunni and Shia Muslims displacing millions of people.

Maliki has been accused by Iraq's Sunni minority – who held sway under the dictatorship of Saddam Hussein – of doing little to re-empower them, or to address their basic demands. Sunni leaders say the Anbar insurgency is making it easier for supporters of Maliki's Shia-led government to disregard their interests.

The war across the border in Syria is fuelling the Anbar insurgency, which has taken on a regional dimension. Senior Iraqi officials talk of the Syrian war as an existential menace.

"It is, of course, of concern for all the nations of the region," said Hussein Shahristani, the deputy prime minister for energy. "Battle-experienced, international terrorists have been able to get political support and financial help from some countries. It has made them a serious security threat to us all, including Iraq.

"The regime committed strategic mistakes in the way they dealt with legitimate demands. This was a tragic and grave error. Those protests that started in Deraa three years ago gave the opportunity for popular resentment at the handling of the crisis.

"Now we have to face the current reality. How can we protect the people from being held hostage to such an extremist threat?"

Iyad Allawi, a former prime minister, said: "All of us are frightened by this. It is becoming very frustrating to see things moving in the wrong direction in all countries."

Allawi, a secular Shia with cross-sectarian appeal, fought a close race with Maliki in 2010, emerging with a similar primary vote that included large numbers of Sunnis. He was unable to form a majority coalition, eventually yielding to Maliki after 10 months of wrangling. This time around, he says he is running a low-profile campaign.

"I am appealing to the dignified people from across Iraq, from Irbil to Basra. We are trying to explain to those who stood against us last time exactly what is happening. We will not deal with those who laid their hands on the wealth of the nation. We are not being supported by any country. We have not stolen," he said.

"The judiciary here is controlled by the executive. We cannot accept a new dictatorship."